As disclosed in the patent document Japanese unexamined patent application publication No. 2005-209278, there have been some well-known library apparatuses (referred to as data storage systems, etc. in some cases) that include a plurality of cells for loading data cartridges respectively. FIG. 5 shows an external perspective view of such a conventional library apparatus.
As shown in FIG. 5, the conventional library apparatus includes two magazines 1200 provided with a plurality of cells 1300 for loading data cartridges 1100 disposed horizontally one upon another respectively; two drive units 1600 for reading/writing data on the recording medium provided in each of the data cartridges 1100; and an accessor 1400 for transferring those data cartridges 1100. The two magazines 1200 are disposed so that the openings of their cells 1300 come to face each other. The accessor 1400 includes a swivel that rotates a picker 1500 that loads/unloads the data cartridges 1100.
The conventional library apparatus, which is configured as described above, is thus capable of loading many data cartridges in its limited space. In this case, however, each cell 1300 can load just one data cartridge 1100. And naturally, the library apparatus is required to manage presence/absence of loading spaces in those cells, as well as the total number of loaded/unloaded cells.
If each cell can load just one data cartridge as described above, a photosensor (not shown) provided for the picker is usually used to check each cell for empty. Concretely, the picker moves to the front of each cell sequentially and emits a light into the cell from its photosensor to judge that the cell is loaded if receiving a predetermined reflection in response of the emitted light. If not, the picker judges that the cell is not loaded. This detection uses a mechanism that a predetermined reflected light can always be detected from the data cartridge if a data cartridge is loaded in the cell. And when a loaded cell is detected, the picker judges that the cell has no loading space and when an empty cell is detected, the picker judges that the cell has a loading space. Then, the picker totals the number of loaded cells and the total number of empty cells.
If each cell can load only one cell, it is just required to detect whether or not each cell is loaded, thereby it is easy to total the number of empty cells. In this case, therefore, another method is available; for example, it is possible to read the bar-code label stuck on each data cartridge to judge whether or not there is any empty cells and total the number of empty cells according to the result.
On the other hand, in recent years, library apparatuses that have employed another cell structure referred to as the deep-cell system have appeared on the market. FIG. 1 shows a top view of a layout of such a library apparatus that has employed the deep-cell system. FIG. 2 shows an external perspective view of a magazine that has employed the deep-cell system. As shown in FIG. 2, the deep-cell system is characterized in that each cell can load a plurality of data cartridges. In case of the layout shown in FIG. 1, the accessor that does not require the swivel described above comes to further reduce the installation place of the library apparatus.